This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
A Brayton cycle engine commonly known as a gas turbine can be adapted to combust fuel at near stoichiometric conditions with exhaust gas recirculation. Such an engine is referred to as an ultra-low emission technology (ULET) because the emissions produced by the engine are primarily inert gases with low contaminant contents. Some ULET engines use the exhaust heat of the gas turbine to produce multiple pressure levels of superheated steam that is used in a condensing steam turbine to produce additional shaft power. In PCT Application Publication No. WO2012003079, such an arrangement is described and referred to as combined cycle power generation (CCPG). A power plant that implements CCPG is referred to as a combined cycle power plant or, simply, a combined cycle plant. Gas turbine combined cycle plants are rather efficient and can be operated at relatively low cost when compared to other technologies, such as coal and nuclear.
The steam turbine in a combined cycle plant runs most efficiently with high quality, i.e., dry, steam. Production of dry steam requires a water feed that is substantially free of contaminants, such as minerals, salts, and silica. Although water is produced as a byproduct of the combustion process in a ULET engine, this water is of low quality and is therefore not readily usable by a boiler of the steam turbine. The cost of purifying the water is often prohibitive and, therefore, the water is often simply discarded. Moreover, although the steam turbine in a combined cycle plant produces blowdown water, this water is also of low quality and is, therefore, discarded in many instances.
In addition, although using the exhaust heat of the gas turbine to produce additional shaft power instead of merely venting it improves overall efficiency of the combined cycle plant, there may be more economical uses for the exhaust heat. However, current combined cycle plants are not equipped to use the exhaust heat or the steam produced with the exhaust heat for any alternative purposes.
For example, U.S. Pat. No. 4,271,664 to Earnest discloses a turbine engine with exhaust gas recirculation. The engine has a main power turbine operating on an open-loop Brayton cycle. The air supply to the main power turbine is furnished by a compressor independently driven by the turbine of a closed-loop Rankine cycle which derives heat energy from the exhaust of the Brayton turbine. A portion of the exhaust gas is recirculated into the compressor inlet during part-load operation. However, no additional uses are disclosed for the exhaust heat or the steam produced with the exhaust heat.